Flu activity continues late-season climb

Feb 17, 2012 (CIDRAP News) – Flu activity in the United States, Canada, and parts of Europe continues to increase, but for the most part, levels of both mild and severe illness are low compared with past flu seasons, the World Health Organization (WHO) said today.

Activity appears to have peaked in a few Northern Hemisphere locations, such as some countries in Western Europe, North Africa, and northern China, according to the WHO.

The H3N2 virus is still dominating in most parts of the world except for Mexico, which is seeing mainly the 2009 H1N1 virus, and China and its neighbors, which are reporting mostly influenza B.

The WHO said that although the 2009 H1N1 virus is circulating at low levels in most parts of the world, in Canada it is having a greater impact on children younger than 5 compared with seniors and in Europe it is responsible for a greater portion of hospitalizations for severe infections.

Flu activity in the United States continued its steady late-season rise last week, with the number of respiratory specimens testing positive for the virus rising from 10.5% to 15.5%, the US Centers for Disease Control and Prevention (CDC) said today. Some flu activity markers were still below their thresholds, including the percentage of deaths from pneumonia and flu and the percentage of doctor's visits for flulike illness.

California, as in the previous week, was the only state that reported widespread flu activity. Twelve states reported regional geographic spread, up from nine the week before.

The CDC received another report of a pediatric flu death, which occurred the week of Jan 21 and involved influenza B. The latest fatality raises the total for the season to three.

So far the H3N2 virus is still the dominant US strain, though 2009 H1N1 and influenza B strains are co-circulating, the CDC said. Of the small numbers of viruses that have been antigenically characterized, about 54% of the influenza B viruses are from the Yamagata lineage, which is not a component of the seasonal flu vaccine.

The CDC cautioned that globally the circulating influenza B strains are similar to the vaccine and that it's too early in the season to assess how well the vaccine matches the circulating strains.

The agency said it expects a continued increase in flu activity in the coming weeks.

Flu activity in Europe continued a slow but steady rise, with 17 countries reporting rising trends, the European Centre for Disease Prevention and Control (ECDC) said today. So far the spread of flu is showing significant variations in timing across the continent, without any clear geographic progression. Seven countries reported widespread flu transmission: Belgium, France, Italy, Norway, Portugal, Slovenia, and Spain.

Except for the Christmas and New Year holiday season, last week was the first time officials saw no rise in the number of respiratory specimens testing positive for influenza. The H3N2 virus is still the dominant strain across Europe, and ECDC lab analysis of flu isolates so far has found no resistance to neuraminidase inhibitors.